1

Ch 3 Atomic Structure and the Periodic Table

Figure 3.1 size relationship is not to scale, ratio of average diameters atom/nucleus = 105

2

Atoms are very small and spherical. Radii Range 0.9 x 10-10 to 2.4 x 10-10 m 90 – 240 pm

Recall Figure 1.12

Atomic Mass example: 1 H atom = 1.673 x 10-24 g 1atomic mass unit (amu) = 1.6605 x 10-24 g For H: 1.673 x 10-24 g x 1 amu . 1.6605 x 10-24 g = 1.008 amu

3

Ch 3.1 Internal Structure of an Atom

Subatomic particles

An atom is characterized by the number of protons (p) that it contains. A proton has a positive electrical charge. p charge = 1.60 x 10-19 coulombs = +1 relative charge p mass = 1.6726 x 10-24 g = ______ amu A neutron (n) has no charge associated with it. n mass = 1.6750 x 10-24 g = ______ amu An electron (e) has a negative electrical charge. e charge = - 1.60 x 10-19 coulombs = -1 relative charge e mass = 9.109 x 10-28 = _________ amu mass of p ~ mass of n >>> mass of e-

mass of e- is often ignored

4

Ch 3.2 Atomic Number and Mass Number Atomic number = Z = # of protons (unique physical property of each element) Mass number = A = # of protons + # of neutrons # of neutrons = ___________ For a neutral atom, net electrical charge = zero

# of electrons = # of protons = _____ A

E complete chemical symbol notation Z

5

A 23

E Na Z 11 # p = Z = ____ # n = A – Z = ________ = ____ # e- = # p = ____

6

Ch 3.3 Isotopes and Atomic Masses Isotopes are atoms of an element that have the same number of protons and electrons but different numbers of neutrons. 12 13 14

C C C 6 6 6 • isotopes have nearly identical chemical

properties

• most elements have at least two isotopes

7

Table 3.2 Elements with Z = 1 through 12

The atomic mass of an element is the calculated weighted average mass for the isotopes.

8

Chem 101 Grading Scheme Quizzes 180 points 180/1000 = 0.18 Labs 160 points 160/1000 = 0.16 Exams 660 points 660/1000 = 0.66 1000 1.00 Sample calculation of weighted average Quizzes 85 % x 0.18 = 15.3 % Labs 95 % x 0.16 = 15.2 % Exams 55 % x 0.66 = 36.3 % Average ___% ____ % Weighted Average

9

35 37

Cl Cl 17 17 34.96885 amu 36.96590 amu 75.77 % 24.23 % natural abundance

atomic mass of Cl = weighted average mass for the isotopes

34.96885 x 75.77/100 = 25.60 36.96590 x 24.23/100 = 8.957 35.46 amu 63 65

Cu Cu 29 29 62.9298 amu 64.9278 amu Atomic weight Cu = 63.546 amu Which isotope is the more abundant? Answer:

10

Ch. 3.4 The Periodic Law and the Periodic Table

Figure 3.2 Dmitri Ivanovich Mendeleev (1834-1907) In 1869 grouped 63 known elements in 1st periodic table based on atomic weights and similar properties within a group.

Modern periodic law - when elements are arranged in order of increasing atomic number, elements with similar chemical properties occur at periodic intervals. Figure 3.4

11

Periods of Elements Figure 3.3

Periods # of elements 1 2 H, He 2 + 3 8 4 + 5 18 6 + 7 > 18 Groups of Elements (Ch 3.4 & 3.9)

Groups IA – VIIIA representative elements IA alkali metals

IIA alkaline earth metals VIIA halogens VIIIA noble gases IB – VIIIB transition metals Outside rows inner transition elements lanthanides & actinides Note: The noble gases are also representative elements.

12

Ch. 3.5 Metals and Nonmetals

Metals Semimetals/Metalloids Nonmetals Semimetals/Metalloids

Used in semiconductors. They have physical properties closer to those of metals, whereas their chemical properties are closer to those of nonmetals.

13

Fig 3.5 solids at RT, except Hg metallic luster malleable & ductile high thermal & electrical ___________ Al Pb Sn Zn clockwise from left

Fig 3.5 gas or solid at RT, except Br2 variety of colors solids are brittle poor __________ (except graphite) good _________ (except diamond) nonductile S8 Br2 P4

14

Ch 3.6 Electron Arrangements within Atoms

Supplemental material: Line Spectra and the Bohr Atom Each element has a unique line spectrum

demo: noble gas discharge tubes

15

Bohr Model Energies of electrons are quantized = limited to certain values. An “excited” atom releases energy in form of light when an electron “falls” back to its lower orbit (ground state).

16

It is now known that electrons do not exist in planet-like orbits but rather they occupy regions of space about the nucleus called orbitals.

Figure 3.8 shapes of orbitals

The space in which electrons move rapidly about a nucleus is divided into shells, subshells, and orbitals.

17

Electron Shells

• are specific energy levels n = 1, 2, 3, 4……… → increasing average distance from nucleus increasing average energy of shells

• electrons occupy the lowest shell available

• max # of electrons allowed in a shell = ______ n = 1 2 e-

n = 2 8 e- n = 3 18 e- etc. Drill question: Where are the electrons of Mg located?

Z = 12 12 p = 12 e-

1st shell (n = 1) = 2 e 2nd shell (n = 2) = 8 e 3rd shell (n = 3) = ___ e

18

Electron Subshells • Each shell (n) consists of subshells

• Subshells are designated s, p, d, f …..

• Energy levels increase s < p < d < f

• Max # of subshells = n (shell)

1st shell n = 1 s 2nd shell n = 2 s + p 3rd shell n = 3 s + p + d 4th shell n = 4 s + p + d + f

• Max # of electrons in subshells s = 2 e p = 6 e d = 10 e f = 14 e

19

Figure 3.7 Summary so far

20

Drill Problems 1. What is the max # of electrons in a 5 d subshell?

Shell # (n) → 5 d ← subshell

max # for d always ____ e, regardless of n 2. What is the max # of electrons in the 4th shell?

s = 2 p = 6 d = 10 f = 14 total: 32 e

also can use: 2 n2 = 2 (4)2 = 32 e

21

Electron Orbital is a region of space within a subshell where an electron with a specific energy is most likely to be found. max of 2 e can be found in 1 orbital subshell # of e # of orbitals s 2 1 p 6 3 d 10 5 f 14 7

22

Characteristics of Orbitals:

• Each type has a specific shape.

Fig 3.8 • Within the same subshell, orbitals differ mainly in

orientation.

Fig 3.9

• Within a given subshell each orbital has the same _____________.

• Volume, average distance, and energy increase with increasing shell number (n).

• Electrons move rapidly and “occupy” the entire orbital volume.

• A pair of electrons in the same orbital must be of opposite ______.

23

Electron Spin

Clockwise “spin up” ↑

Counterclockwise “spin down” ↓

A pair of electrons of opposite spin can occupy the same orbital but electrons prefer to be alone – Hund’s Rule Ch 3.7 Electron Configurations and Orbital Diagrams • fill lower energy levels first • for a given subshell, first place single electrons • pair electrons only with opposite spins

1s2 2s2 2p6 3s2 3p3 Electron Configuration for P: 1s22s22p63s23p3 Shorthand representation for P: 1s22s22p63s23p3 = [Ne]3s23p3

24

Electron-Dot Symbols

6C ↑↓ ↑↓ ↑ ↑ _ 1s 2s 2px 2py 2pz 1s22s22p2 ___ unpaired electrons

Electrons in the s & p orbitals of the outermost shell (valence shell) are called valence electrons and can be shown in an electron-dot symbol or Lewis symbol (also see Chapter 4.2) For the isolated (non-bonded) carbon atom: 4 valence electrons in the 2nd shell 2 valence e in s are paired, 2 e in p are unpaired

. . · C · • all 4 sides in the symbol are equal • unpaired electrons must be shown as single dots • paired electrons must be shown as pairs

25

8O ↑↓ ↑↓ ↑↓ ↑ ↑ 1s 2s 2px 2py 2pz 1s22s22p4 2 unpaired electrons For the isolated (non-bonded) oxygen atom: ___ valence electrons in the 2nd shell ___ valence e paired, ___ e unpaired

. . : O ·

· Note: The group number of the representative elements corresponds to the ___________ of valence electrons in the element

26

Fig 3.10 Order of filling electron subshells

27

Figure 3.11 Mnemonic device for remembering subshell filling order

28

Ch 3.8 The Electronic Basis for the Periodic Law and the Periodic Table 3Li 1s22s1 11Na 1s22s22p63s1 19K 1s22s22p63s23p64s1 37Rb 1s22s22p63s23p64s23d104p65s1 Group IA ___ valence electron in s orbital 9F 1s22s22p5 17Cl 1s22s22p63s23p5 35Br 1s22s22p63s23p64s23d104p5 53I 1s22s22p63s23p64s23d104p65s24d105p5 Group VIIA ___ valence electrons s2 & p5

29

Figure 3.12 Electron configuration and the position of elements in the periodic table.

30

31

32

Supplemental Material & Ch 5.9

Properties of Atoms and the Periodic Table

A. Chemical properties of an element are related to the position of an element in the periodic table. demo: compare reactivity of Li, Na, K, Ca, Mg with H2O same same similar group = valence = chemical electrons properties

33

B. Periodic trends in metallic character for representative elements.

• Metallic character increases with increasing shell number (n) in a group.

• It decreases with increasing number of valence electrons.

34

C. Periodic trends in atomic radii (pm) for representative elements.

• Within a group, radii increase with increasing shell

number (i.e. increasing distance from the nucleus).

• Across a period, radii decrease as the number of protons in the nucleus increase (i.e. increasing nuclear charge).

35

D. The type and number of bonds an element forms are related to its position in the periodic table. Electronegativity is a measure of the relative attraction that an atom has for the shared electrons in a covalent bond.

Figure 5.11 in Stoker

very different values → __________ bonds Chapter 4 similar values → ___________ bonds Chapter 5

36

E. Periodic trends in ionization energies for representative elements. Li · → Li+ + e- neutral atom positive ion electron cation Ionization of atoms requires Ionization Energy (I.E.) • Within a period I.E. increases with increasing Z.

• Down a group I.E. decreases with increased atomic radius.